When drilling a wellbore, fluids in the underground formation surrounding the wellbore are under pressure. In order to prevent their flow into the wellbore, drilling fluid, commonly known as drilling mud, is introduced into the wellbore. The hydrostatic pressure of the drilling mud against the wellbore may be used to prevent the fluid from entering the wellbore. When the hydrostatic pressure of the drilling mud equals the formation pressure, the drilling operation is typically referred to as balanced. Typically, a wellbore is drilled slightly overbalanced, such that the hydrostatic pressure of the drilling mud is higher than the formation pressure.
However, if the hydrostatic pressure of the drilling mud falls below the formation pressure, an underbalanced condition, fluid from the formation may flow into the wellbore. This increase in fluid flow is known as a kick. If a kick is not contained, a blowout may occur. Kicks may be caused by insufficient mud weight, improper hole fill-up during trips, swabbing, gas cut mud, or lost circulation. In order to reduce the risk of blowouts, drilling rigs utilize pressure control devices such as blow out preventers, choke manifolds, Kelly-Cocks, and flapper discs.
In some drilling operations, a rotating control device may be utilized to route drilling mud returning up the annulus of the wellbore to mud process equipment. The RCD may seal against the wellbore and the rotating drill string which passes therethrough. An RCD may be used during, for example, managed pressure drilling in which the hydrostatic pressure of the drilling mud may be monitored and actively regulated based on encountered conditions in the wellbore.